To explore the molecular mechanism of exocytosis in the nerve terminal we wish to identify, isolate and characterize the synaptic vesicle and the presynaptic plasma membrane. We have already developed a procedure for obtaining highly purified synaptic vesicles from the electric organs of Narcine brasiliensis, with good yields. To gain some insight into the mechanism of membrane fusion we shall investigate both the membrane asymmetry of the synaptic vesicles, examining the distribution of lipid, protein and carbohydrate and also the specific binding of calcium to the outside of vesicles. To explore the synthesis and turnover of vesicles proteins, we shall label the proteins of the nerve terminals by rapid axonal transport. To generate immunocytochemical markers for synaptic vesicles we shall prepare antibodies to pure synaptic vesicles and to their individual proteins. Such markers may be of value in specifically identifying the presynaptic plasma membrane which is the first step to isolation. We will also examine conditions for non-destructive labeling of the presynaptic neruotoxin, beta-bungarotoxin, for use as a specific probe of plasma membranes, taking advantage of our detailed knowledge of the toxin's biochemistry and mechanism of action.